[Patent Literature 1] JP 2005-228225 A
[Patent Literature 2] JP 2002-24043 A
For example, Patent Literature 1 discloses a technology, which avoids a system break-down due to a failure in update of firmware in a memory card adapter containing a rewritable flash memory. Specifically, a flash memory additionally includes a non-rewriting area which stores a program that permits minimum operation even when the firmware update under the onboard state is unsuccessful. Further, the non-rewriting area is additionally provided with a function to determine success or failure of the result of the firmware update. At a restart after completing the firmware update, the processing jumps to the non-rewriting area by an interrupt vector function, thereby activating an update result determination means that is stored in the non-rewriting area for determining the success or failure of the result of the firmware update. When the result is successful, the processing jumps to the start address of the main program, starting an operation by the new firmware. In contrast, when the result is unsuccessful, the firmware is updated again.
Further, Patent Literature 2 discloses a microcomputer, which enables the rewriting of an interrupt vector table even when adopting onboard rewriting of a flash memory, eliminating the restrictions on development of a user program. To that end, an address control circuit is additionally provided in between the CPU and the flash memory in order to provide the flash memory with an alternative reset vector address which specifies a storage position of the start address of a rewrite control program, by replacing a reset vector address that is outputted from the CPU so as to specify the start of the vector table. This configuration can start an execution of the rewrite control program using indirect addressing based on the alternative reset vector address outputted from the address control circuit, thereby rewriting the vector table along with a user program.
In the technology of Patent Literature 1 the interrupt vector function is not erased at the time of the firmware update; thus, the program stored in the non-rewriting area can be executed using the interrupt vector function even after the firmware update. This configuration cannot change the contents of the interrupt vector function, unfortunately. Therefore, an assigned address of an interrupt processing program specified by the interrupt vector function cannot be changed as needed even at the time of upgrading the version of the main program.
In contrast, the technology in Patent Literature 2 can rewrite the vector table along with the user program (i.e., main program), enabling the change of the assigned address of an interrupt processing program as needed. Adopting the indirect vector addressing using such a vector table can reduce the data size of the whole program, providing an advantage.
However, the technology of Patent Literature 2 provides the above-mentioned address control circuit in between the CPU and flash memory for outputting an alternative reset vector address. Providing such a dedicated circuit for outputting the reset vector address, instead of a vector table, complicates the circuit configuration of the microcomputer, increasing costs.